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I agree with Curtis ... and if you include the DRQ bit in the mix (sff8020),
you get a bigger picture of the current bus phase. How is this confusing?
Or not usefule?
IO DRQ CoD What it means
-- --- ---
-----------------------------------------------------
0 1 1 Command - Ready to Accept Command Packet Bytes
1 1 1 Message (Future) - Ready to Send Message data to
Host
1 1 0 Data To Host- Send command parameter data (e.g. Read
Data) to the host
0 1 0 Data From Host - Receive command parameter data
(e.g.
Write Data) from the host
1 0 1 Status - Register contains Completion Status
Regards,
Mark
-----Original Message-----
From: Curtis Stevens [mailto:[EMAIL PROTECTED]]
Sent: Tuesday, February 12, 2002 10:35 AM
To: [EMAIL PROTECTED]
Subject: RE: [t13] doing a big favor
Hale
The way IO and CD get used really depends on the design of the host.
Since there is no CRC or Checksum on the command you send to the drive,
there is no real way to validate that the right hing is happening. IO and
CD give you at least some confirmation that the right thing is happening.
Further, if the host side is designed with independent state-machines to
read data and to send commands the IO and CD bits become very important. I
am aware of some firmware that works this way... The firmware is not broken
because IO and CD are well defined in the specification as to how they
operate during data transfers.
-----------------------
Curtis E. Stevens
Pacific Digital Corp.
2052 Alton Parkway
Irvine, CA 92606
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